Background: Rapid socioeconomic development resulting in changing lifestyles and life expectancy appears to be accompanied by an increasing prevalence of type 2 diabetes. Genetic predisposition related to ethnicity is a major determinant of diabetes risk. This study investigates the prevalences of diabetes and prediabetes in different ethnic populations residing in the Mudanjiang area located in the northeast of China. Methods: A cross-sectional survey was carried out among Han, Manchu and Korean Chinese aged 20 years or older. Diabetes and prediabetes were diagnosed using standard oral glucose tolerance tests. Results: The prevalence of diabetes in Manchu (8.39%) and Korean Chinese (9.42%) was significantly lower than that in Han (12.10%). The prevalence of prediabetes was 18.96%, 19.36% and 20.47% in Han, Manchu and Korean populations, respectively. Korean Chinese had a lower prevalence of isolated impaired fasting glucose and higher prevalence of isolated impaired glucose tolerance than the other two ethnic groups. Most patients with diabetes, especially ethnic minority patients, were undiagnosed. A multiple logistic regression analysis showed that age, family history of diabetes, control of diet, self-monitoring of weight, central obesity, increased heart rate, hypertension, elevated plasma triglyceride level, elevated plasma low-density lipoprotein cholesterol, and Han ethnicity were significantly associated with an increased risk of diabetes. Further, Manchu Chinese were found to have the lowest risk of diabetes. Conclusions: Our study indicates that diabetes is a major public health problem in the Mudanjiang area of China. Ethnicity plays a role in the different prevalences of diabetes and prediabetes among the three ethnic groups. Diabetes is less prevalent among Manchu Chinese compared with Han and Korean Chinese.